Perito Moreno Glacier Geography and the Retreat

For about eighty years this glacier held its position while almost every other one on Earth pulled back. That is no longer true, and the change was measured, published and dated.

Hours, prices and access verified by the Perito Moreno Glacier Tours team — last checked August 10, 2026.

Where the ice comes from

Perito Moreno drains the Southern Patagonian Ice Field, a body of roughly 13,000 square kilometres straddling the Argentina–Chile border and one of the largest non-polar ice masses on the planet. Pacific weather systems dump enormous snowfall on its western flank. That accumulation fed the glacier for decades and is the reason it behaved so differently from its neighbours.

The glacier itself runs about 30 kilometres from the ice field to its terminus, with a front roughly 5 kilometres wide and a surface area near 250 square kilometres. The ice wall stands somewhere between 60 and 74 metres above the lake depending on the source and the point measured, with about 170 metres more below the waterline.

The lake and the dam

The terminus runs into Lago Argentino, Argentina’s largest lake, at the point where two arms meet: Brazo Rico to the south and the Canal de los Témpanos to the north. When the ice front pushes far enough across, it seals Brazo Rico off from the main body of the lake.

Cut off, the southern arm has nowhere to drain. Its level rises — historically by tens of metres — until the pressure forces a tunnel through the ice at the contact point. The tunnel widens, the roof thins, and eventually an arch of ice collapses into the channel. That is the rupture, and it is the event people travel here hoping to catch. It cannot be scheduled.

Why it stayed stable

What held the front in place was a pair of factors. Snowfall on the ice field replaced what melted at the terminus, and the glacier grounded against a submerged rocky ridge that stopped it retreating into deeper water. A glacier that stays grounded loses ice slowly. One that floats free loses it fast.

What changed in 2019

Research published in Communications Earth & Environment in August 2025 by Moritz Koch, Pedro Skvarca and Lucas Ruiz put numbers on a shift that guides had already noticed.

That is a sixteen-fold acceleration. Alongside it the team recorded faster ice flow and frontal retreat of roughly 700 metres a year between 2021 and 2023, concentrated on the northern margin. Copernicus satellite imagery from June 2026 shows the front well behind where it sat in 2016.

Using helicopter-borne radar and bathymetric survey, the study mapped the bed beneath the ice and found the front now close to flotation over that protective ridge. Their model tests what happens if current thinning continues: once the ice recedes past the ridge and floats, buoyancy-driven retreat can take over and run much faster. The paper does not name a year. Every path it tested points the same way.

How the rupture actually works

The dam is not a metaphor. When the ice front touches the Magallanes Peninsula it seals Brazo Rico off from the rest of Lago Argentino, and because Brazo Rico keeps receiving meltwater with nowhere to go, its level climbs — by as much as thirty metres above the main lake in the largest recorded events.

Water under that head of pressure finds a way through. It works into the base of the ice, opens a tunnel, and enlarges it as it flows. The tunnel becomes a passage, the passage becomes an arch, and eventually the arch cannot hold its own roof. The collapse is the spectacle, and it lasts minutes.

The interval between ruptures has run from under two years to more than a decade. Nobody can date the next one, and any tour that implies otherwise is selling weather.

Why the ice is that blue

Snow falling on the ice field is buried and compressed until the air is squeezed out of it. Bubble-free ice behaves like deep water: it absorbs the long red wavelengths and scatters the short blue ones back out. That is why the deepest blues sit inside crevasses and freshly calved faces, where the ice is oldest and densest, and why the same glacier reads plain white where fresh snow lies on top.

It is also why a flat, overcast Patagonian day is often the better one for photographs. Direct sun floods the surface and washes the colour out.

What the 2025 study measured

Koch, Skvarca and Ruiz published frontal-lowering figures in Communications Earth & Environment in August 2025 that put the change beyond argument: 0.34 metres per year between 2000 and 2019, and 5.5 metres per year from 2019 onward. That is roughly sixteen times faster.

The retreat is uneven. The northern margin has pulled back on the order of 700 metres a year between 2021 and 2023, while the southern side has held far better. The visitor consequence is small so far — the wall you photograph is still five kilometres of ice — but the equilibrium that made this glacier famous has ended, and the figures are on the key facts page.

What this means for a visit

Very little, in the short term. The ice front is still a wall five kilometres wide, calving happens daily, and the walkways look out on the same spectacle they always did. Ruptures continue to occur, though the interval between them has never been regular.

What has changed is the story. This is no longer the glacier that defied the trend; it is a glacier that held out longer than most and is now behaving like the rest of Patagonia. Upsala and Viedma, both visible on the Lago Argentino cruises, have been retreating for decades. Perito Moreno has joined them.